Hemithyroidectomy is the preferred initial operative approach for an indeterminate fine needle aspiration biopsy diagnosis

Thyroid nodules are common in the general population; they are identified in about 5% of patients by palpation and 50% by ultrasound examination.1 Fine needle aspiration biopsy (FNAB) represents the critical initial diagnostic test used for evaluation of thyroid nodules. However, in a large number of patients, the distinction between benign and malignant thyroid nodules has remained challenging for clinicians. In a review of more than than 18 000 thyroid FNABs carried out at the Mayo Clinic in Rochester, Minn., FNAB had a reported sensitivity of 83%, specificity of 92% and accuracy of 95%.2 Furthermore, in up to 15% of patients, the preoperative diagnosis of cancer was classified as indeterminate or suspicious for cancer.2–6 Indeterminate cytological diagnoses occur for follicular patterned thyroid lesions owing to overlapping cytomorphologic characteristics of benign and malignant lesions.2,3 In these patients, pathologic evaluation of the tumour specimen is required to identify additional tumour characteristics, such as the presence of capsular or vascular invasion, for an accurate diagnosis of cancer. Furthermore, the cytological evaluation of FNAB specimens of papillary carcinoma can often be challenging owing to differences in the interpretation of the required threshold of nuclear change for a cancer diagnosis.6 The major diagnostic criteria for papillary thyroid carcinoma (PTC) include an irregular and enlarged nucleus, eccentric micronucleoli, fine chromatin, longitudinal nuclear grooves and intranuclear pseudoinclusions. However, thyroid FNAB specimens can have some, but not all, of the features required to fulfill the cytological diagnostic criteria required for a cancer diagnosis. Such lesions may be classified as being “suspicious” or “highly suspicious” for cancer.4 There is also substantial inter- and intraobserver variability in cytological and pathological assessment of follicular patterned thyroid lesions.7 Thus, when an individual presents with a thyroid nodule and an FNAB cytological diagnosis of Hurthle cell neoplasm (HN), or an aspirate suspicious for papillary carcinoma, the current recommended approach of the American Thyroid Association is removal of either a portion of or the entire thyroid gland.8 Furthermore, in patients with follicular neoplasms (FN) diagnosed by FNAB, radioiodine thyroid imaging may be considered, and a diagnostic lobectomy or total thyroidectomy is recommended especially in individuals with nonfunctioning nodules.8 Total thyroidectomy carries a low but increased risk of permanent hypoparathyroidism and the need for lifelong calcium supplementation as well as increased risk for bilateral recurrent laryngeal nerve dysfunction and subsequent possible need for a lifelong tracheostomy compared with thyroid lobectomy. Some individuals will also require lifelong thyroid hormone replacement therapy. Surgical series have reported malignancy rates of 13%–30% for patients with FN9–13 and 21%–42% for those with HN.14–16 At our centre, a thyroid lobectomy and isthmusectomy is performed as the initial operation for patients with an indeterminate cytological diagnosis and no clinical evidence of regional or distant metastatic disease or any other concurrent indication for total thyroidectomy (i.e., goitre, Graves disease). If gross extrathyroidal tumour extension or lymph node metastasis is found at the time of operation, a total thyroidectomy is then carried out. Intraoperative frozen section examination is not used in our management approach for FN or HN, but may be used for other cytologically indeterminate nodule types at the discretion of the operating surgeon. Consistent with the current literature, in prior reports of our experience, only about 1 in 5 patients undergoing thyroid operation for FN or HN were eventually found by histopathologic evaluation to have cancer.17,18 Hemithryoidectomy was considered to be adequate definitive treatment in 96% of individuals with FN and 82% with HN diagnosed preoperatively with FNAB cytology. The present study was carried out with the aim of evaluating our current algorithm for the surgical treatment of thyroid nodules in a large prospectively collected patient cohort. Thus, our review represents a real-world experience of the treatment of thyroid nodules at a regional Canadian tertiary endocrine surgical referral centre. The aim of the study was to determine the optimal surgical approach for individuals presenting with a cytologically indeterminate thyroid nodule. We sought to determine the cytological distribution, the utility of clinicopathological characteristics for predicting malignancy and the true proportion of cancer among individuals with indeterminate cytology who undergo thyroid operation.